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Abstract:
All rodents investigated so far possess orientation-selective neurons in the primary
visual cortex (V1) but – in contrast to carnivores and primates – no evidence of pe-
riodic maps with pinwheel-like structures. Theoretical studies debating whether
phylogeny or universal principles determine development of pinwheels point to
V1 size as a critical constraint. Thus, we set out to study maps of agouti, a big diurnal
rodent with a V1 size comparable to cats’. In electrophysiology, we detected inter-
spersed orientation and direction-selective neurons with a bias for horizontal con-
tours, corroborated by homogeneous activation in optical imaging. Compatible
with spatial clustering at short distance, nearby neurons tended to exhibit similar
orientation preference. Our results argue against V1 size as a key parameter in
determining the presence of periodic orientation maps. They are consistent with
a phylogenetic influence on the map layout and development, potentially reflecting
distinct retinal traits or interspecies differences in cortical circuitry.
